At present, with the accelerating urbanization process, more and more people rush into cities, which puts an increasing strain on urban land. Therefore, more buildings have to be built underground, for example, underground parking lots, underground warehouses, and underground restaurants. Of course, many facilities are built underground in view of factor of safety, for example, large-scale underground oil storage and military installations. These are typical examples of underground buildings. Once these underground buildings have a failure, it is difficult to detect a location where the failure occurs. Definitely, difficulty in detection exists not only in urban underground buildings, but also in other aspects such as archaeology, mineral prospection, engineering thermophysics, and dam detection. By this token, underground building detection has great significance in terms of civil use. Therefore, it is necessary to carry out research on detection and identification of underground buildings.
At present, underground building detection studied by scholars worldwide is mainly based on a passive infrared imaging detection technology. The physical basis of this technology is that a lot of solar energy is absorbed by the irradiated soil and produces heat, and the heated soil generate infrared radiation that is detected by an infrared sensor. Natural solar energy, through daily cyclical heating and cooling, produces different effects on a buried object and soils surrounding the buried object, leading to a detectable temperature difference. The existence of an underground building may cause land surface water/heat distribution abnormity, which can be used to detect, discover, verify, and confirm the underground building.
The infrared imaging technology is used by scholars worldwide to detect an underground building. However, the existing infrared imaging sensors studied by the scholars are directly used for imaging, and the obtained infrared image is interpreted manually, which causes great limitation. The limitation lies in that: First, the unusual heat of the underground building is conducted and modulated by the stratum in which the underground building is buried, and when the heat reaches the land surface, the heat distribution changes significantly compared with that for the underground building, which is embodied by a severe thermal diffusion, a significant decrease in a temperature difference, and a weak thermal signal. Secondly, after the conduction and modulation by the stratum, a location of the underground building, which is represented by the land surface thermal signal, may have changed, and it is difficult to find and position the underground building. Thirdly, manual interpretation is difficult, and is unfavorable to accurate detection and positioning of the underground building.